VAPOUR ABSORPTION REFRIGERATION SYSTEM BY: ASHLAR ALI 3rd SEMESTER BE MECHANICAL

INTRODUCTION An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling system. A vapor absorption system makes use of a substance, called absorbent to absorb large volumes of the vapor of a refrigerant even when cold and reduce it to a liquid, and subsequently give off its vapors when heated.

TYPES: 1> Single pressure absorption system Uses lithium bromide salt as absorbent & water as refrigerant. 2> Water spray absorption system 3> Simple absorption system Uses ammonia as refrigerant & water as absorbent.

PRINCIPLE: The absorption cooling cycle can be described in three phases: Evaporation: A liquid refrigerant evaporates in a low partial pressure environment, thus extracting heat from its surroundings – the refrigerator. Absorption: The gaseous refrigerant is absorbed – dissolved into another liquid - reducing its partial pressure in the evaporator and allowing more liquid to evaporate. 3. Regeneration: The refrigerant-laden liquid is heated, causing the refrigerant to evaporate out. It is then condensed through a heat exchanger to replenish the supply of liquid refrigerant in the evaporator.

Figure shows the schematic diagram of a vapor absorption system Figure shows the schematic diagram of a vapor absorption system. Ammonia vapor is produced in the generator at high pressure from the strong solution of NH3 by an external heating source. The water vapor carried with ammonia is removed in the rectifier and only the dehydrated ammonia gas enters into the condenser. High pressure NH3 vapor is condensed in the condenser. The cooled NH3 solution is passed through a throttle valve and the pressure and temperature of the refrigerant are reduced below the temperature to be maintained in the evaporator. The low temperature refrigerant enters the evaporator and absorbs the required heat from the evaporator and leaves the evaporator as saturated vapor. Slightly superheated, low pressure NH3 vapor is absorbed by the weak solution of NH3 which is sprayed in the absorber as shown in Figure. Weak NH3 solution (aqua–ammonia) entering the absorber becomes strong solution after absorbing NH3 vapor and then it is pumped to the generator through the heat exchanger. The pump increases the pressure of the strong solution to generator pressure. The strong NH3 solution coming from the absorber absorbs heat form high temperature weak NH3 solution in the heat exchanger. The solution in the generator becomes weak as NH3 vapor comes out of it. The weak high temperature ammonia solution from the generator is passed to the heat exchanger through the throttle valve. The pressure of the liquid is reduced to the absorber pressure by the throttle valve.

ADVANTAGES : DISADVANTAGES: >Less noise. >Can be used for above 1000 ton capacity. >Corrosion problem is less. >Maintenance cost is low. DISADVANTAGES: >Low COP. >Only ammonia can be used as refrigerant. >Bulky in size.

APPLICATIONS: Used in evaporator coolers. Widely used in cold storage, ice making plants. In oil refineries , chemical plants, recreational vehicles.

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